Estimating a source location of a projectile

ABSTRACT

According to examples of the presently disclosed subject matter, there is provided a system for estimating a source location of a projectile, comprising an optics an optics subsystem, a radar subsystem and a processor. The processor is adapted to use range and velocity measurements obtained from data provided by the radar subsystem, a source direction and an event start time obtained from data provided by the optical subsystem and a predefined kinematic model for the projectile for estimating a range to a source location of the projectile.

FIELD OF THE INVENTION

The present invention is in the field of optical and radar signal processing.

REFERENCES TO RELATED PUBLICATIONS

Fusion of optics and radar was discussed in the following publications:

-   [1] Langer D., Jochem T., “Fusing radar and vision for detecting,     classifying and avoiding roadway obstacles,” Proc. of Conf. on     Intelligent Vehicles (2000) -   [2] Blackman S. S., Dempster R. J., Roszkowski S. H., Sasaki D. M.,     Singer P. F., “Improved tracking capability and efficient radar     allocation through the fusion of radar and infrared search-and-track     observations,” Optical Engineering 39(5), 1391-1398 (2000) -   [3] A., Kester L., van den Broek S., van Dorp P., and van Sweeden     R., “The FRESNEL Program: Fusion of Radar and Electro-optical     Signals for Surveillance on Land,” Proc. SPIE 4380, 453-461 (2001) -   [4] Kester L. and Theil A., “Fusion of Radar and EO-sensors for     Surveillance,” Proc. SPIE 4380, 462-471 (2001) -   [5] A. Gem, U. Franke, and P. Levi, “Robust vehicle tracking fusing     radar and vision,” in Proc. Int. Conf. Multisensor Fusion Integr.     Intell. Syst., 323-328 (2001) -   [6] Birkemark C. M. and Titley J. D., “Results of the DRIVE I     experiment for fusion of IR and Radar Data,” Proc. SPIE 4380,     472-479 (2001) -   [7] B. Steux, C. Laurgeau, L. Salesse, and D. Wautier, “Fade: A     vehicle detection and tracking system featuring monocular color     vision and radar data fusion,” in Proc. IEEE Intell. Vehicles Symp.,     632-639 (2002) -   [8] Y. Fang, I. Masaki, and B. Horn, “Depth-based target     segmentation for intelligent vehicles: Fusion of radar and binocular     stereo,” IEEE Trans. Intell. Transp. Syst. 3(3), 196-202 (2002) -   [9] Scholz T. K., Förster J., “Environmental characterization of the     marine boundary layer for electromagnetic wave propagation”, Proc.     SPIE 4884, 71-78 (2003) -   [10] Whitehead P. G., Bernhardt M., Hickman D., Dent C., “Range and     brightness fusion: using radar and electro-optical data association     for tracking small objects,” Proc. SPIE 5096, 423-431(2003) -   [11] N. Kawasaki and U. Kiencke, “Standard platform for sensor     fusion on advanced driver assistance system using Bayesian network,”     Proc. IEEE Intell. Vehicles Symp. 240-255 (2004) -   [12] N. Yonemoto, K. Yamamoto, and K. Yamada, “A new color, IR, and     radar data fusion for obstacle detection and collision warning,”     Proc. SPIE 5424, 73-80 (2004) -   [13] Schultz J., Gustafsson U. and Crona T., “Sensor data fusion of     optical and active radar data,” Proc. SPIE 5429, 490-500 (2004) -   [14] Mobus R. and Kolbe U., “Multi-Target Multi-Object Tracking,     Sensor Fusion of Radar and Infrared,” IEEE Intelligent Vehicles     Symposium (2004) -   [15] Amditis A., Polychronopoulos A., Floudas N., Andreone L.,     “Fusion of infrared vision and radar for estimating the lateral     dynamics of obstacles,” Information Fusion 6(2), 129-141 (2005) -   [16] Everett M., Manson D., Brook A., Davidson G., “A Naval Infrared     Search and Track Demonstrator and its fusion with other ship     sensors,” Proc. SPIE 6206, 620626 (2006) -   [17] Gang W., Kun-tao Y., “Discussion on Operating Range of     Shipborne Infrared Search-and-Track System,” Proc. SPIE 6150, 61501V     (2006) -   [18] L Bombini, P Cerri, P Medici, G Alessandretti in Symposium,     “Radar-vision fusion for vehicle detection”, A Quarterly Journal In     Modern Foreign Literatures ( ) 2006 -   [19] Latger J., Cathala T., Douchin N., Le Goff A., “Simulation of     active and passive infrared images using the SE-Workbench,” Proc.     SPIE 6543, 654302 (2007) -   [20] Forand J. L., “Method to estimate infrared and radio-frequency     synergy,” Optical Engineering 46(12), 126001 (2007) -   [21]Y. Tan, F. Han, and F. Ibrahim, “A radar guided vision system     for vehicle validation and vehicle motion characterization,” in     Proc. IEEE Intell. Vehicles Symp., 1059-1066 (2007) -   [22] Feng H., Wan Hai Y., “Radar and Infrared Data Fusion Algorithm     Based on Fuzzy-neural Network,” Proc. SPIE 6723, 67233S (2007) -   [23] de Villers Y., “A fusion study of a range-Doppler imager with     an infrared sensor for ground-to-ground surveillance,” Proc. SPIE     7308, 73081B (2009) -   [24] Wu, S. Decker, S. Chang, P., Camus, T., Eledath J., “Collision     Sensing by Stereo Vision and Radar Sensor Fusion,” IEEE Trans. on     Intelligent Transportation Systems 10(4), 606-614 (2009)

BACKGROUND

Applications which use a fusion of optics and radar include driver assistance, navigation aids, collision avoidance and obstacle avoidance. Yet another important application is land surveillance. At sea, the fusion of optical sensors with radar is used to resolve mirage and signal ambiguity problems above the horizon, and to allow for fine accuracy target tracking. Air-to-Air target detection and tracking using airborne IRST and Fire-Control-Radar (FCR) is also known. The brightness of target signal data was also used to resolve the location of adjacent targets along with the radar data.

FIG. 1 is a table which compares various characteristics of existing optical detection units and corresponding characteristics of existing radar detection units.

SUMMARY

Many of the functional components of the presently disclosed subject matter can be implemented in various forms, for example, as hardware circuits comprising custom VLSI circuits or gate arrays, or the like, as programmable hardware devices such as FPGAs or the like, or as a software program code stored on an intangible computer readable medium and executable by various processors, and any combination thereof. A specific component of the presently disclosed subject matter can be formed by one particular segment of software code, or by a plurality of segments, which can be joined together and collectively act or behave according to the presently disclosed limitations attributed to the respective component. For example, the component can be distributed over several code segments such as objects, procedures, and functions, and can originate from several programs or program files which operate in conjunction to provide the presently disclosed component.

In a similar manner, a presently disclosed component(s) can be embodied in operational data or operational data can be used by a presently disclosed component(s). By way of example, such operational data can be stored on tangible computer readable medium. The operational data can be a single data set, or it can be an aggregation of data stored at different locations, on different network nodes or on different storage devices.

The method or apparatus according to the subject matter of the present application can have features of different aspects described above or below, or their equivalents, in any combination thereof, which can also be combined with any feature or features of the method or apparatus described in the Detailed Description presented below, or their equivalents.

According to an aspect of the presently disclosed subject matter, there is provided a system for estimating a source location of a projectile. According to examples of the presently disclosed subject matter, a system for estimation a source location of a projectile can include a optics subsystem, a radar subsystem and a processor. The processor can adapted to use range and velocity measurements from the radar subsystem, a source direction and an event start time from the optical subsystem and a predefined kinematic model for the projectile to estimate a range to a source location of the projectile.

According to a further aspect of the presently disclosed subject matter, there is provided a method of estimating a source location of a projectile. According to examples of the presently disclosed subject matter, the method of estimating a source location of a projectile can include: using a range and velocity measurements from a radar subsystem, a source direction and an event start time from an optical subsystem and a predefined kinematic model for the projectile for estimating a range to a source location of the projectile.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to understand the invention and to see how it may be carried out in practice, a preferred embodiment will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:

FIG. 1 is a table which compares various characteristics of existing optical detection units and corresponding characteristics of existing radar detection units;

FIG. 2 is a block diagram illustration of an implementation of a system for estimating a source location of a projectile, according to examples of the presently disclosed subject matter;

FIG. 3 is a flowchart illustration of an algorithm that can be used to control the operation of a system for estimating a source location of a projectile according to examples of the presently disclosed subject matter;

FIG. 4 is a graphical representation of the example-case projectile kinematic model (speed and range vs. time—assuming the projectile is flying directly at the system), according to examples of the presently disclosed subject matter;

FIG. 5 is a graphical representation of the results of computation of the 3rd type algorithm, where the horizontal axis is a radar subsystem velocity measurement error and the vertical axis is a correction to that error calculated by minimizing the model fit errors as described above, for the test case scenario, according to examples of the presently disclosed subject matter; and

FIG. 6 is a graphical representation of the launch event range estimation error distribution, as calculated by means of a Monte-Carlo simulation of the operation of each one of the three suggested algorithms with the scenario/system parameters defined in Table-1, according to examples of the presently disclosed subject matter.

It will be appreciated that for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity. Further, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements.

DESCRIPTION

In the following description, numerous specific details are set forth in order to provide a thorough understanding of the disclosed subject matter. However, it will be understood by those skilled in the art that the disclosed subject matter can be practiced without these specific details. In other instances, well-known methods, procedures and components have not been described in detail so as not to obscure the presently disclosed subject matter.

Unless specifically stated otherwise, as apparent from the following discussions, it is appreciated that various functional terms can refer to the action and/or processes of a computer or computing device, or similar electronic device, that manipulate and/or transform data represented as physical, such as electronic quantities within the computing device's registers and/or memories into other data similarly represented as physical quantities within the computing device's memories, registers or other such tangible information storage, transmission or display devices.

The term “projectile” is known in the art, and the following definition is provided as a non-limiting example only for convenience purposes. Accordingly, the interpretation of the term projectile in the claims, unless stated otherwise, is not limited to the definition below, and the term “projectile” in the claims should be given its broadest reasonable interpretation. Throughout the description and in the claims, reference is made to the term “projectile”. The term “projectile” as used here relates to an object that is launched projected, ejected, fired, etc., and where the launch, projection, ejection or firing of the projectile has an optical signature which is detectable by an optical detection unit or subsystem. For example, the optical signature can be associated with a muzzle flash or an ignition of a propellant, which is approximately coincident with the time of the launch projection, ejection, firing of the projectile. For convenience, the term launch is used herein to describe any event that is associated with the launch, projection, ejection or firing of the projectile and which is substantially coincident with the optical signature that is detected by the optical subsystem, as further described herein.

It would be appreciated that the projectile can be powered or not, and that the projectile can be guided or unguided.

Throughout the description and in the claims, reference is made to the terms “source location”. The terms “source location” as used here relates to the location of the optical signature that is associated with the launch, projection, ejection or firing of the projectile which was detected by the optical subsystem.

According to examples of the presently disclosed subject matter, the projectile can be approximately or accurately headed towards a predefined point of interest. For example, the projectile can be approximately or accurately headed towards the system which is used to estimate a source location of a projectile. Still further by way of example, the projectile can be approximately or accurately headed towards a radar subsystem which is used by the system.

According to an aspect of the presently disclosed subject matter, there is provided a system for estimating a source location of a projectile. It would be appreciated that the system, which is described below in further details can be a stationary or mobile. For example, the system can be mounted on a vehicle traveling on land (e.g., a car, a truck, etc.), at sea (e.g., a ship), in the air (e.g., a helicopter, an aircraft, etc.) or in space.

According to examples of the presently disclosed subject matter, the system can include an optics subsystem, a radar subsystem and a processor. The optics subsystem can be configured to detect a launch of the projectile within predefined range limits from the system. Based on data related to the launch from the optical subsystem, the processor can be configured to obtain an event start time and a source direction. The processor can be configured to provide the radar subsystem with initialization settings that are based on the source direction and the event start time.

The radar subsystem can be configured to operate according to the initialization settings to obtain range and velocity measurements for the projectile at a given instant. The processor can be configured to use the range and velocity measurements from the radar subsystem, the source direction and the event start time from the optical subsystem and a predefined kinematic model for the projectile for estimating a range to the source location.

According to examples of the presently disclosed subject matter, the processor can be configured to determine the source location based on the estimated range to the source location and based on the source direction. In still further examples of the presently disclosed subject matter, the processor is configured to determine the source location further based on a self location of the system. By way of example, the system can include a GPS (“Global Positioning Service”) receiver module and/or an INS (“Inertial Navigation System”) module which is configured to provide the self location of the system.

According to examples of the presently disclosed subject matter, in case the system is mobile and is moving during the flight of the projectile, the processor can be configured to take into account the movement of the system when determining the range to the source location and when estimating the source location.

According to examples of the presently disclosed subject matter, the kinematic model can be a relatively naïve approximation which assumes that the projectile's velocity that was measured by the radar at the given instant was constant and was maintained by the projectile from the launch.

According to further examples of the presently disclosed subject matter, based on the projectile's velocity that was measured by the radar at the given instant, the processor can be configured to perform a mathematical backward extrapolation of the projectile's velocity down to the event start time.

According to still further examples of the presently disclosed subject matter, the processor can be configured to further take into account predefined or conditions dependent operational parameters of the system or of any of its components and/or predefined or conditions dependent environmental parameters when determining the range to the source. For example, the processor can be configured to take into account a predefined or conditions dependent random noise level and/or predefined or conditions dependent bias errors.

In still further examples of the presently disclosed subject matter, the processor can be configured to take into account further predefined or conditions dependent operational parameters of the system or of any of its components and/or predefined or conditions dependent environmental parameters, including for example: an optical geometrical distortion of the optical subsystem optics, a line of sight misalignment between the radar subsystem and the optics subsystem, an optical subsystem response spatial (angular) non-uniformity, report latency and delays, an optical spot Centroid estimation, etc.

In yet further examples of the presently disclosed subject matter, the processor can be configured to further take into account predefined operational parameters of the system or of any of its components and/or environmental parameters (e.g. air temperature wind velocity and direction and air pressure) in order to calculate a certainty range and direction boundaries for the source location. In yet further examples of the presently disclosed subject matter, the system can include one or more of the following: a wind-velocity sensor, an air temperature sensor and a (air) pressure sensor. Still further by way of example, one or more of the wind-velocity sensor, the air temperature sensor and the (air) pressure sensor can sense certain environmental conditions related to the operation of the system, and environmental parameters which are associated with the environmental conditions that were sensed by the sensors can be taken into account by the processor at least when processing measurements from the optics subsystem or from the radar subsystem.

In still further examples of the presently disclosed subject matter, the radar subsystem can be configured to obtain a plurality of range and velocity measurements for the projectile at a plurality (two or more) of different instants during the flight of the projectile, and the processor can be configured to use the plurality of range and velocity measurements for estimating the range to the source location. In addition to the plurality of range and velocity measurements, the processor can be configured to use the source direction, the event start time and a predefined kinematic model for the projectile and possibly also predefined or conditions dependent operational parameters of the system or of any of its components and/or predefined or conditions dependent environmental parameters for estimating the range to the source location. According to examples of the presently disclosed subject matter, in case the system has no a-priori knowledge of the type of projectile, the processor can be configured to assume, in parallel, multiple kinematic models, calculate their back projection extrapolation, and then choose the one(s) that best match the measured data.

According to examples of the presently disclosed subject matter, the predefined kinematic model for the projectile can consist of multiple (two or more) phases. According to examples of the presently disclosed subject matter, two or more different phases of the kinematic model for the projectile can be associated with a different velocity of the projectile. Further by way of example, the different velocity of the projectile can be based on an assumption of a certain acceleration/deceleration of the projectile during different periods of its flight.

According to still further examples of the presently disclosed subject matter, the processor is configured to implement a minimum velocity threshold, and in case the measured velocity of the projectile is determined to be less than the minimum closing-in velocity threshold the projectile is considered be non-threatening. Further by way of example, in case the projectile is considered to be non-threatening, the system terminates all operations relating to the projectile.

According to still further examples of the presently disclosed subject matter, the processor is configured to assume a bias error and/or a random velocity error in respect to the radar's measurements.

According to yet another aspect of the presently disclosed subject matter there is provided a method of estimating a source location of a projectile. According to examples of the presently disclosed subject matter, the method of estimating a source location of a projectile can include: detecting using an optical subsystem a launch of the projectile within predefined range limits from the system; obtaining an event start time and a source direction based on data related to the launch from the optical subsystem; providing a radar subsystem with track-initialization settings which are based on the source direction and the event start time; obtaining using the radar subsystem range and velocity measurements for the projectile at a given instant; and estimating a range to the source location based on the range and velocity measurements from the radar subsystem, the source direction and the event start time from the optical subsystem and based on a predefined kinematic model for the projectile, or a library of possible kinematic models.

Further examples of the presently disclosed subject matter are implementations of the herein disclosed operations carried out by the components of the system which combines optical sensing and radar sensing to estimate a source location of a projectile, but are not necessarily carried out by the respective components of the herein disclosed system. Rather in some examples of the presently disclosed subject matter, the method can be implemented using any suitable hardware, computer implemented software and any suitable combination of hardware and computer implemented software.

Further examples of the presently disclosed subject matter are now described.

Reference is now made to FIG. 2, which is a block diagram illustration of an implementation of a system for estimating a source location of a projectile, according to examples of the presently disclosed subject matter. According to examples of the presently disclosed subject matter, the system 100 can include an optics subsystem 10, a radar subsystem 20 and a processor 30.

According to examples of the presently disclosed subject matter, the optics subsystem 10 can be configured to detect a launch of the projectile within predefined range limits from the system 100 or from the optics subsystem 10. Projectile launch detection using optics is known per-se and any suitable optics subsystem and method can be used for detecting the launch of the projectile. For illustration purposes there are now provided non-limiting examples of optics that can be used for detecting the launch of the projectile:

According to an example of the presently disclosed subject matter, the optics subsystem can include a detection module that utilizes potassium (K) doublet emission lines (e.g. ˜760 nm) or Sodium (N) emission lines detection with contrast to adjacent optical spectrum narrow bands which lack this emission from flash, plume and fire radiance.

According to a further example of the presently disclosed subject matter, the optics subsystem can include a detection module that utilizes the contrast between “Red-band” (within MWIR 4.4 um-4.9 um spectral band) and other MWIR sub-bands as evident in flash, plume and fire radiance.

According to yet a further example of the presently disclosed subject matter, the optics subsystem can include a detection module that utilizes solar blind UV (SBUV) emission from flash, plume and/or fire radiance—with contrast to natural and/or artificial scene background which lack significant radiance in the SBUV band.

According to still a further example of the presently disclosed subject matter, the optics subsystem can include a detection module that utilizes LWIR spectral band radiance emitted from flash, plume and fire radiance.

According to a further example of the presently disclosed subject matter, the optics subsystem can include a detection module that utilizes significant blackbody and/or molecular (e.g. H2O) emission in the SWIR (1.0 um-2.5 um) optical spectral band with contrast to other optical sub-bands (e.g. visible [0.4 um-0.7 um], NIR [0.7 um-1.0 um]) in which same emission is essentially lower, using one or more sensors dedicated to different spectral sub-bands.

Those versed in the art have the knowledge that is necessary to provide an optics subsystem which includes the appropriate sensors for detecting a projectile lunch according to the examples provided herein.

Based on data related to the launch from the optics subsystem 10, the processor 30 can be configured to obtain an event start time and a source direction. The processor 30 can be configured to provide the radar subsystem 20 with initialization settings that are based on the source direction and the event start time. The radar subsystem 20 can be configured to operate according to the initialization settings to obtain range and velocity measurements for the projectile at a given instant. The processor 30 can be configured to use the range and velocity measurements from the radar subsystem 20, the source direction and the event start time from the optical subsystem and a predefined kinematic model for the projectile for estimating a range to the source location.

It would be appreciated that in a temporally and spatially aligned system, e.g., where the optics subsystem 10 and the radar subsystem 20 measurement reports are temporally and spatially aligned, estimating of the range to the source location based on the event start time and the source direction (which are obtained based on data related to the launch from the optics subsystem 10), and based on the range and velocity measurements (which are obtained based on data from the radar subsystem 20), and further based on the predefined kinematic model for the projectile, can be carried out using techniques and equipment which are known per-se to those versed in the art.

It would be appreciated that according to examples of the presently disclosed subject matter, the optics subsystem 10 and the radar subsystem 20 can have an accurate common (and/or otherwise synchronized) timing, It would be also appreciated that according to examples of the presently disclosed subject matter, the optics subsystem 10 and the radar subsystem 20 can be aligned so as to allow co-registration of the directions of the optics subsystem LOS and the radar subsystem LOS and towards a detected event (e.g. azimuth and elevation).

Examples of techniques which can be implemented to achieve accurate common timing, and examples of techniques which can be implemented to allow co-registration of the directions of the optics subsystem and the radar subsystem LOS and towards a detected event are now disclosed, as part of examples of the presently disclosed subject matter.

As mentioned above, according to examples of the presently disclosed subject matter, the co-operation among the optics subsystem 10 and the radar subsystem 20 requires precise alignment and registration of the directions towards a detected event (azimuth and elevation) as reported by the two subsystems.

According to examples of the presently disclosed subject matter, the co-registration is made to be substantially accurate at every field direction within the common field of view of the detection subsystems (e.g., the optics subsystem and the radar subsystem). Further by way of example, a misalignment angular error (pitch, roll, and yaw) between different detection subsystems (e.g., the optics subsystem and the radar subsystem) can be precisely registered and then—direction finding reports (Azimuth, Elevation) within the FOV of each of the detection subsystems (e.g., the optics subsystem and the radar subsystem) can be precisely measured and registered.

According to examples of the presently disclosed subject matter, co-registration of the optics subsystem and the radar subsystem directions (and possibly additional detection subsystems if exist) can involve mechanically aligning the LOS (or a similar indicator of the direction of the FOV) of the optics subsystem and the radar subsystem and possibly additional detection subsystems if they exist).

According to examples of the presently disclosed subject matter, the co-registration of the optics subsystem and the radar subsystem (and possibly additional detection subsystems if they exist) can further include providing as similar as possible FOVs for the optics subsystem and the radar subsystem (and possibly additional detection subsystems if exist), such that the FOV that is common to the optics subsystem and to the radar subsystem (and possibly to additional detection subsystems, if they exist) is substantially maximized with respect to the detection subsystems overall FOV solid angle. In this regard, it should be appreciated that the field of regards or FORs (i.e.—the scene sector, in Earth coordinates, regarded by the sub-system's FOV, considering the direction of its center (LOS)) of the detection subsystems should have a common part as dictated by the system level requirement. In order to avoid increasing the individual detection subsystem FOVs (as a possible means to compensate for mismatch between LOS directions)—which could complicate the detection subsystem design and/or decrease its performance (e.g. detection range, FAR etc.), the Line Of Sights (LOSs) of the detection subsystems should be aligned as much as possible taking into account the operational and other practical circumstances.

A further co-registration operation which can be implemented according to examples of the presently disclosed subject matter, can include utilizing high accuracy measurement of the angular FOV deviations between the detection subsystems (e.g., the optics subsystem and the radar subsystem), and the geometrical mapping between directions reported by the detection subsystems and the true direction towards a detected event by same detection subsystems. These measurements can be used to compensate for any direction finding (DF) errors using calculations which are known per se. It would be appreciated that the latter co-registration calibration operation can be effective within a FOV which is common to the detection subsystems, and on-condition that the components (mechanics, electronics and optics) of the detection subsystems are stable enough to a certain degree (which reflects the required co-registration accuracy), until the next co-registration calibration measurement is carried out.

It would be appreciated that according to examples of the presently disclosed subject matter, as part of the co-registration of the detection subsystems referencing of their source location report to an external, global direction (e.g. azimuth w.r.t magnetic north, geographic north etc., elevation w.r.t true horizon, nadir etc.) can be carried out. The below examples, describe calibration techniques and methods which can be implemented as part of examples of the presently disclosed subject matter. It would be appreciated that if the location of the calibration objects is known wrt to a global reference, then the calibration techniques described herein can readily be used for global referencing. Descriptions of examples of techniques and methods for measuring a single field angle are followed by descriptions of examples of techniques and methods for measuring of multiple field angles.

According to examples of the presently disclosed subject matter, a radar calibration objection object (e.g., a radar reflector) can be positioned at a range large enough to be considered as far-field for the radar subsystem, and the radar calibration object is co-positioned with an optical calibration object (e.g., a light emitter) which is configured to provide (e.g., emit, reflect, etc.) an optical signal at spectral band(s) in which the optics subsystem is substantially sensitive to incoming optical signals. By way of example, in order to maximize the contrast and SNR of measurement of the direction towards the optical calibration object, a light emitter can be provided which has an amplitude and/or a phase and/or a frequency that is modulated such that most of the generated optical signal is given off in a narrow frequency, phase bandwidth, and/or during short periods of time (narrow pulses), in order to allow for complete measurement of the angular deviation.

A further example of a technique that can be used for calibration (or local direction referencing) is similar to the calibration technique which was described in the preceding paragraph, with the following modification: the positioned calibration objects (e.g., radar reflector and light emitter) can be placed at known locations (e.g., the locations can be measured with measurement units other than the detection subsystems which are being calibrated), and the detection subsystems being calibrated (e.g., the optics subsystem and the radar subsystem) can also be located at a well known geographic position. In this manner—the viewing directions from the detection subsystem towards a detected object(s) can be calculated off-line (or on-line) and used to correct for the DF reports of each one of the detection subsystem, and to compensate for any error(s).

A further example of a technique that can be used for calibration is similar to the calibration technique which was described in each of the two preceding paragraphs, and further including implementing an image processing algorithm to reduce the errors induced by atmospheric path (between the detection subsystems that are being calibrated and a target(s)) turbulence, and/or for optical abberations in the optics of the optics subsystem.

Yet a further example of a technique that can be used for calibration is similar to the calibration technique which was described above, but in this example, the optical calibration object is not artificially introduced in the FOV but rather it is some object which is part of the scenery. For example, the optical calibration object can be detected automatically using an image processing algorithm, for example processing algorithms which implement feature extraction in the digital imagery signals or similar techniques, and which can be used for example to detect building edges, polls, antenna towers etc., based on predefined criteria. Still further by way of example, once the optical calibration object is detected and selected for use, a direction towards a feature of the object (e.g. edge, center, maximum brightness location) can be measured. The feature can also be selected automatically based on predefined logic and/or algorithms Yet further by way of example, the radar calibration object can be installed in a vicinity of the optical calibration object. Still further by way of example, if one of the radar subsystem or the optics subsystem already calibrated (was calibrated in a different time or setting), then only the other (yet to be calibrated) subsystem should be calibrated.

In yet a further example, that can be used for calibration and is similar to the calibration technique which was described above, but as an optical calibration object, an object, onto which a grid of light or structured light (e.g., a 2D spatial pattern of light) is projected, is used. The structured light projection can be configured to enable reflection of light toward the optics subsystem in the optical sensitivity spectrum of the optics subsystem. The Radar calibration object can be positioned with relation to the object onto which the structured light is projected, e.g., in the same location or in a location that is substantially adjacent to the optical calibration object.

According to some examples of the presently disclosed subject matter, the optics subsystem can include a projector that is configured to project the structured light, and thus in such an example, the structured light can be created by the optics detection subsystem itself (e.g.—by projecting light onto the imaged scenery). In yet a further example, the source of the structured light is external to the optics subsystem.

As mentioned above, in addition to the co-registration of the optics subsystem and the radar subsystem, accurate common timing of measurements may also be required as part of some examples of the presently disclosed subject matter. Examples of techniques and methods which can be implemented as part of examples of the presently disclosed subject matter to achieve accurate common timing are now described.

According to examples of the presently disclosed subject matter, a common timing reference for the optics subsystem and the radar subsystem can be obtained by:

(a) a GPS timing signal as received and analyzed by a GPS receiver which can be implemented as part of either one of the optics subsystem or the radar subsystem or externally to these subsystems, within the system.

(b) a clock signal which can be generated by either one of the optics subsystem or the radar subsystem and can be transmitted to the other subsystem as a reference. Counters in either one of the optics subsystem or the radar subsystem or in both subsystems can be used to count a number of clock signal pulses in order to establish cumulative time counting.

In a further example, a common (external) timing reference for both the optics subsystem and the radar subsystem can be avoided by allowing one of the optics subsystem or the radar subsystem to act as a “master” with respect to the other subsystem (which will act as a “slave”). In this configuration the slave subsystem can be configured to respond to messages sent by the master, as demonstrated in two different implementations below:

(a) a time code message can be generated by either one of the optics subsystem or the radar subsystem which acts as a master. The time code is communicated to the slave subsystem, which is responsive to receiving the time code for responding the master subsystem with a message that contains information about the slave subsystems measurements (e.g. velocity, range, azimuth, elevation, launch event etc.) and a respective time code which indicates the time difference between the time of receipt of the time code message and the time of the measurements in respect of which data is included in the response message.

(b) in this implementation, either one of the subsystems or both can operate a timer. One of the optics subsystem or the radar subsystem, which for convenience will be referred to now as the first subsystem, can be configured to accumulate the counts of its own timer, while whenever the first subsystem performs a measurement it can be configured to send a reset command to the second subsystem's timer. In this way, when the second subsystem reports its measurement results (e.g., to the first subsystem), the counting status of the second subsystem's local timer that is attached to the report indicates the lag between the measurement time of the first subsystem and that of the second subsystem. It would be appreciated that this technique can nullify any drifts that could have otherwise accumulated over time between the two clocks (or timers) running separately without coordination in the first and the second subsystems (even if these clocks had, in theory, the same counting rate (e.g. frequency)).

It would be appreciated that accurate knowledge of the instance of time, relative to a common (local) time reference, in which the optics subsystem and the radar subsystem make their respective measurements can be implemented in the system to decrease projectile's origin (launcher, barrel, etc.) location estimation errors. For instance, if the projectile measurement at the time it is detected by the radar subsystem is V [m/s] and the relative timing error between the optics subsystem and the radar subsystem is dt [sec], then the resulting launcher location error may be as large as V×dt [m]. Since high-energy kinetic projectile velocity can reach 1740 m/s (e.g. General Dynamics KEW-A1, see http://en.wikipedia.org/wiki/Kinetic_energy_penetrator) 20 m accuracy may require timing accuracy of better than 10 ms which suggests yet better accuracy at each and every part of the timing mechanisms described above—as the accumulated error must stay less than 10 ms.

Having described the spatial and temporal alignment of the optics subsystem 10 and the radar subsystem 20, there are now provided further details according to examples of the presently disclosed subject matter, with respect to the implementation of the various components of the system 100.

According to examples of the presently disclosed subject matter, the optics subsystem 10 can include an optical detection unit 12 and a signal processor 14. It would be appreciated that this is a simplified illustration of an optics subsystem 10, and that various optics subsystems in different configurations can be used as part of the system for estimating a source location of a projectile 100 according to examples of the presently disclosed subject matter. By way of example, the optics subsystem 10 can include one or more optical detection channels, each of which can be imaging or non imaging, each of which can include optical spectral filters, an optical lens or lenses, an optical detector, detector analog and digital readout electronics, nd-filters and mechanics to mount, support and stabilize the optics and other components of the optics subsystem. Each channel can also include a cooling unit and/or a temperature stabilization module for the detector and for any other component of the channel.

According to examples of the presently disclosed subject matter, the signal processor 14 of the optics subsystem 10 can be configured to perform an initial processing of the signals generated by the optical detection unit 12 and can provide the detection data mentioned herein to the processor 30 for further processing.

According to examples of the presently disclosed subject matter, the radar subsystem 20 can include a transmitter receiver unit transceiver 22 and a signal processor 24. It would be appreciated that this is a simplified illustration of a radar subsystem 20, and that various radar subsystems in different configurations can be used as part of the system for estimating a source location of a projectile according to examples of the presently disclosed subject matter. By way of example, the radar subsystem 20 can include an antenna (or an array of antennae) or an array of antennae or a phase array antennae, a low noise amplifier, a modulator, a demodulator, switches and diplexer. It would be appreciated that in some examples of the presently disclosed subject matter, any reference made herein to components of the system can also refer to multiple units of each component, as appropriate.

According to examples of the presently disclosed subject matter, the signal processor 24 of the radar subsystem 20 can be configured to perform an initial processing of the signals generated by the transmitter receiver unit 22 and can provide data related to the measurements preformed by the radar subsystem 20 to the processor 30 for further processing.

According to examples of the presently disclosed subject matter, the system 100 can further include a GPS receiver module 40 and/or an INS module 50. The GPS 40 or INS 50 can provide the self location of the system 100, and the processor can use the self location data to determine the location of the source location of the projectile.

In still further examples of the presently disclosed subject matter, the system 100 can further include a cover case (not shown). For example, the cover case can house at least the optics subsystem 10 and the radar subsystem 20. Still further by way of example, the cover case can be adapted to protect the optics subsystem 10 and the radar subsystem 20 against external environmental conditions (e.g. rain, hail, dust, wind etc.). Still further by way of example, the cover case can include an aperture or apertures which are transparent to radar EM signals (RADOME) and transparent to optical wavelengths. Thus for example, the cover case can enable common installation of the optics subsystem 10 and the radar subsystem 20 behind a common mechanical aperture. An example of an aperture that can be used in the cover case is described in US Patent Publication 2012/0038539, which discloses an integrated radio frequency (RF)/optical window that includes an RF radome portion provided from a composite material substantially transparent to RF energy disposed about an optical window configured for use with an optical phased array, and which is hereby incorporated by reference in its entirety.

Further in connection with the cover case, and according to examples of the presently disclosed subject matter, it would be appreciated that the optics subsystem 10 includes optical elements (e.g. in lenses), optical filters, attenuators, windows and other types of optical quality surfaces, and can be sensitive to humidity in general and to condensation in particular, which can compromise the surface quality of the optical elements surfaces. According to examples of the presently disclosed subject matter, in order to avoid or reduce the effects of such condensation, the cover case can provide a controlled atmosphere (dry and clean) therewithin at least where the optics subsystem 10 is installed. For example, the cover case can include a chamber for housing the optics subsystem 10, and the environmental conditions within the chamber can be controlled. It would be appreciated that the controlled atmosphere chamber can contribute towards size and weight reduction of the system 100.

Further, as would be appreciated by those versed in the art, operation of the active part of the radar antenna and associated electronics can generate RFI and EMI at the optics subsystem's 10 electronics. Thus, according to examples of the presently disclosed subject matter, the chamber in which the optics subsystem 10 is installed within the cover case, can be well isolated from the interferences created by the operation of the radar subsystem 20, in order to mitigate such interferences (e.g. Faraday cage can be used). Still further by way of example, the electrical leads (power supplies, signal wires etc.) of the optics subsystem 10 can be isolated from the conducted and emitted interference as generated by the radar subsystem 20.

There is now provided a description of certain predefined models which can be implemented by the processor 30 to determine the source location of the projectile. It would be appreciated that according to examples of the presently disclosed subject matter, other models can be implemented by the processor 30 to determine the source location of the projectile. In further examples of the presently disclosed subject matter, certain details of the models set forth below can be adjusted or modified or omitted from the model that is implemented by the processor and/or the models set forth below can be expanded with additional computations.

According to examples of the presently disclosed subject matter, the processor 30 can be configured to implement a predefined kinematic model of the projectile. According to examples of the presently disclosed subject matter, the predefined kinematic model of the projectile assumes that the launch of the projectile occurs at t=0. An expression for the muzzle velocity can be included in the kinematic model, for example the expression

$v_{{nom}\; 1} \pm {\delta\;{v_{1}\left\lbrack \frac{m}{s} \right\rbrack}}$ can be included in the kinematic model, where v_(nom1) is the nominal velocity and δv₁ is an associated uncertainty.

According to examples of the presently disclosed subject matter, the kinematic module can assume that at an instant which can be denoted by t=T₁ the projectile starts accelerating (or de-accelerating) at a linear rate with time. The kinematic model can further assume that at t=T₂ this acceleration (or de-acceleration) ends, and at which point the projectile is at a velocity that can be denoted by

${v_{{nom}\; 2} \pm {\delta\;{v_{2}\left\lbrack \frac{m}{s} \right\rbrack}}},$ where v_(nom2) is a nominal velocity and δv₂ is an associated uncertainty.

Following t=T₂ and until t=T₃ the kinematic model can assume a generic deceleration rule based on aerodynamic drag (and assuming the projectile balances gravity with lift and hence does not change its altitude) as can be denoted by the expression F_(d)=½ρ·v²C_(d)·S, where ρ is the air density [kg/m³], v is the projectile velocity [m/s], C_(d) is the drag coefficient and s is the projectile cross section area [m²]. Assuming a constant air density ρ, a nonlinear declaration rule can be derived:

$\alpha = {\frac{dv}{dt} = {\left. {K \cdot v^{2}}\rightarrow{\int\frac{dv}{v^{2}}} \right. = {\left. {\int{K \cdot {dt}}}\rightarrow{v(t)} \right. = \frac{1}{{K \cdot t} + C}}}}$ ${{v(0)} = v_{2}},{{v\left( {t_{3} - t_{2}} \right)} = v_{3}},{C = {\left. \frac{1}{v_{2}}\rightarrow K \right. = {\frac{1}{v_{2} \cdot v_{3}}{\frac{\left( {v_{2} - v_{3}} \right)}{\left( {t_{3} - t_{2}} \right)}\left\lbrack \frac{1}{m} \right\rbrack}}}}$ where v₃ can denote the projectile velocity at time t=T₃. Since v₃ is a random variable, it can be calculated using the expression:

$v_{3} = {v_{{nom}\; 3} \pm {\delta\;{{v_{3}\left\lbrack \frac{m}{s} \right\rbrack}.}}}$

The complete nominal (no errors) velocity profile of the projectile can be denoted as v₀(t) and the nominal range between the projectile and the source location (the location of the launcher (gun), immediately following the launch can be denoted by R₀(t)=∫₀ ^(t)v₀(τ)dτ.

The kinematic model can be completed by assigning a minimum and maximum launcher to target (the location of the system) range limits which can be denoted by R_(launch_min) and R_(launch_max) respectively.

According to examples of the presently disclosed subject matter, the processor 30 can further implement a model that is related to the radar subsystem 20. According to examples of the presently disclosed subject matter, in accordance with the model which relates to the radar subsystem 20 it can be assumed that:

The range to projectile is smaller a maximum range which can be denoted by R_(max), where R_(max) can vary between a best maximum range which can be denoted by R_(max_best) which indicates the longest possible detection range under the most favorable conditions, and a worst maximum range which can be denoted by R_(max_worst) which indicates the shortest (guaranteed) detection range under the worst case operation conditions.

In order to be considered a valid threat, the projectile's velocity should be greater than a projectile velocity threshold which can be denoted by v_(min) [m/s].

The radar output data can consist of: the range at time t, with associated random error σ_(R) [% RMS] as percentage of the true range, and a bias error μ_(R) [%] (which for convenience is assumed to be zero in the following examples); and the velocity at time t, with associated random error which can be denoted by σ_(v) [% RMS] as percentage of the true velocity, and a bias error which can be denoted by μ_(v) [%] (which for convenience is assumed to be zero in the following examples).

According to examples of the presently disclosed subject matter, the processor 30 can further implement a model that is related to the optics subsystem 10. According to examples of the presently disclosed subject matter, in accordance with the model which relates to the optics subsystem 10 it can be assumed that:

The optics subsystem 10 detects the launch event substantially immediately after it starts. For example, the models for the optics subsystem 10 can assume that the optics subsystem 10 detects the launch event with a possible delay of no more than its video frame time; the optics subsystem's 10 measurements timing is substantially precisely synchronized with the radar subsystem's 20 measurements; the optics subsystem 10 update rate is fast enough to allow for characterizing the detected event and associating it with a launch/ejection/projection/fire event optical signal as opposed to other possible optical sources, as well as fast enough to mitigate the effects brought about by moving (linear and/or angular) of the system and/or of objects in the field of regard of the system. For example—an optical sensor operating in the SWIR band should typically operate at a rate higher than approximately 200 Hz.

In order to demonstrate the capacity of the system according to examples of the presently disclosed subject matter to estimate the location of the projectile launcher, the scenario parameters of Table 1 below are assumed. It would be appreciated that the scenario presented herein below is a mere example of one possible scenario wherein one possible implementation of the system for estimating a source location of a projectile is utilized to estimate the projectile source.

In the below scenario three different algorithms are proposed for calculating the source location based on the measurements carried out in the system according to examples of the presently disclosed subject matter. It would be appreciated that any one of these algorithms can be implemented by the system.

TABLE 1 Case study parameters RADAR 50 [m/s] V_(min) 1500 [m] R_(max)(worst) 2000 [m] R_(max)(best) 10% σ_(v) 10% σ_(R) Projectile 0.15, 1.5, 15 [sec] T₁, T₂, T₃ 20, 300, 160 [m/s] V₁, V₂, V₃ 3000 [m] R_(launch)(max) 1000 [m] R_(launch)(min) 1, 10, 10 [m/s] dV₁, dV₂, dV₃

Assume the projectile is launched at a range denoted by R_(launch) (R_(launch) is within the range limits as set above). The optical subsystem detects the launch event at t₀=0. The radar subsystem measures velocity of the projective and range to the projectile at t=T_(radar) based on the parameters in table-1. A first estimate of the projectile range and velocity is set according to: R_(radar)=R_(m)(T_(radar))+ΔR v_(radar)=v_(m)(T_(radar))+Δv, where R_(m)(T_(radar)) denotes a true range to the projectile at time t=T_(radar), ΔR denotes a radar range measurement error, v_(m)(T_(radar)) denotes a projectile true velocity at t=T_(radar) and Δv denotes a radar velocity measurement error.

Three different estimation algorithms are proposed and each of which can be implemented by the system:

Algorithm 1: Estimate a range from the projectile to the launcher based on a model of projectile range versus time after launch. For example, the following expression can be used to denote this computation: {circumflex over (R)}_(m1)=R₀(t=T_(radar)), {circumflex over (R)}_(launch1)=R_(radar)+{circumflex over (R)}_(m1), where {circumflex over (R)}_(m1) denotes a pre-stored model of the projectile nominal kinematics which assigns a single projectile trajectory path denoted by R₀ for a velocity denoted by v_(m)(T_(radar)).

Algorithm 2: Estimate a projectile-launcher range based on a model of projectile velocity versus time after launch. For example, the following expression can be used to denote this computation: {circumflex over (R)}_(m2)=R₀(t|v₀(t))=V_(radar)), {circumflex over (R)}_(launch2)=R_(radar)+{circumflex over (R)}_(m2).

Algorithm 3: Calculate {circumflex over (R)}_(m1) and {circumflex over (R)}_(m2) using the above computations, and minimize the inconsistencies between the two using variations calculus. For example, the following expression can be used to denote this computation: ∈_(v)=v₀(T_(Radar))−V_(radar), ∈_(R)={circumflex over (R)}_(launch1)−{circumflex over (R)}_(launch2)={circumflex over (R)}_(m1)−{circumflex over (R)}_(m2).

FIG. 3 is a flowchart illustration of an algorithm that can be used to control the operation of a system for estimating a source location of a projectile according to examples of the presently disclosed subject matter. The optics subsystem can detect the event and measures directions towards it, relative to the direction-reference of the optics subsystem. The radar subsystem can search for a projectile at the designated direction. If the system receives information about its own kinematic movement, it updates the search direction accordingly. If the search-time-limit is reached, and a projectile is not found within the search-direction boundaries, the system can discard the event. If a projectile is detected by the radar subsystem within the search-time limit and within the angular search boundaries, then data measured by the radar subsystem is used for calculating the projectile's origin of flight (also referred to herein as the source location). It should be noted that the entire procedure could be reversed—starting with a projectile detection by the radar subsystem, followed by a search through the optics subsystem's data memory for detected launch event at the direction of the detected projectile.

FIG. 4 is a graphical representation of the example-case projectile kinematic model (speed and range vs. time—assuming the projectile is flying directly at the system), according to examples of the presently disclosed subject matter.

FIG. 5 is a graphical representation of the results of computation of the 3rd type algorithm, where the horizontal axis is a radar subsystem velocity measurement error and the vertical axis is a correction to that error calculated by minimizing the model fit errors as described above, for the test case scenario, according to examples of the presently disclosed subject matter. Each point on the chart represents the result of one Monte Carlo simulation. The obvious correlation between error and correction demonstrates the success of the proposed algorithm.

FIG. 6 is a graphical representation of the launch event range estimation error distribution, as calculated by means of a Monte-Carlo simulation of the operation of each one of the three suggested algorithms with the scenario/system parameters defined in Table-1, according to examples of the presently disclosed subject matter.

It will be understood that the system according to the invention may be a suitably programmed computer. Likewise, the invention contemplates a computer program being readable by a computer for executing the method of the invention. The invention further contemplates a machine-readable memory tangibly embodying a program of instructions executable by the machine for executing the method of the invention. 

The invention claimed is:
 1. A system, comprising: an optics subsystem; a radar subsystem; a Faraday cage; a processor; wherein the optics subsystem and the radar subsystem are substantially co-located, and wherein the optics subsystem is installed within said Faraday cage which enables electromagnetic isolation of the optics subsystem from electromagnetic interferences (EMI) and/or radio frequency interferences (RFI) created by operation of the radar subsystem, wherein the optics subsystem comprises a detection module adapted for acquiring at least one of (i) and (ii): (i) a first image in a first optical spectrum band comprising potassium (K) doublet emission lines or Sodium (N) emission lines, and a second image in a second optical spectrum band different from the first optical spectrum band; (ii) a first image in “Red-band” within MWIR spectral band, and a second image in other sub-bands of the MWIR spectral band, different from the “Red-band”; wherein the processor is configured to determine a difference between pixels of the first image and pixels of the second image, wherein the processor is configured to apply feature extraction to imaged scenery captured by the optics subsystem to identify a feature in the imaged scenery and determine a direction towards the identified feature.
 2. The system of claim 1, wherein electrical leads of the optics system are located within the Faraday cage.
 3. The system of claim 1, wherein the optics subsystem and the radar subsystem are co-registered.
 4. The system of claim 1, wherein the optics subsystem and the radar subsystem are timely synchronized.
 5. The system of claim 1, comprising a processor configured for processing measurements from the optics subsystem and the radar subsystem.
 6. The system of claim 5, wherein the processor is configured to utilize measurements from the radar subsystem to process range and velocity measurements for pixels of imaged scenery captured by the optics subsystem.
 7. The system of claim 5, wherein the processor is configured to take into account one or more of the following: an optical geometrical distortion of the optics subsystem, a line of sight misalignment between the radar subsystem and the optics subsystem; an optics subsystem response latency; spatial non-uniformity of the measurements; and an optical spot Centroid estimation of the optics subsystem.
 8. The system of claim 1, wherein the processor is configured to perform co registration operation comprising: obtaining, from the radar subsystem, radar measurements of radar calibration objection object positioned at a far-field range; obtaining, from the optics subsystem, optical measurements of an optical calibration object configured to provide an optical signal at spectral band(s) detectable by the optics subsystem; and utilizing said radar measurements and said optical measurements to determine registration between the radar subsystem and the optics subsystem.
 9. The system of claim 8, wherein said radar calibration objection object is co-positioned with the optical calibration object.
 10. The system of claim 8, wherein said radar calibration objection object and said optical calibration object are placed at different known locations; and wherein the viewing direction of the radar calibration objection object from the radar subsystem, and viewing direction of the optical calibration object from the optics subsystem is used to correct direction findings of the radar subsystem and the optics subsystem, and thereby determine registration between them.
 11. The system of claim 8, wherein said optical calibration object is light emitter providing modulated light; and wherein co-registration operation comprises image processing utilizing said modulation to reduce errors induced by atmospheric path turbulence and/or for optical aberrations of the optics subsystem.
 12. The system of claim 11, wherein said optical calibration object generates optical signal during short periods of time.
 13. A system, comprising: an optics subsystem; a radar subsystem; wherein the optics subsystem comprises one or more cameras configured to acquire at least one of (i) and (ii): (i) a first image in a first optical spectrum band comprising potassium (K) doublet emission lines or Sodium (N) emission lines, and a second image in a second optical spectrum band different from the first optical spectrum band; (ii) a first image in “Red-band” within MWIR spectral band, and a second image in other sub-bands of the MWIR spectral band, different from the “Red-band”; a processor configured for processing measurements from the optics subsystem and the radar subsystem; wherein the processor is configured to: utilize measurements from the radar subsystem to process range and velocity measurements for pixels of imaged scenery captured by the optics subsystem; and determine a difference between pixels of the first image and pixels of the second image captured by the optics subsystem, identify one or more features in the imaged scenery based on said difference, and determine a direction towards the one or more identified features.
 14. A system, comprising: an optics subsystem located at a first position; a radar subsystem located at a second position substantially co-located with the first position; and a processor configured for processing measurements from the optics subsystem and the radar subsystem; wherein the processor is configured to perform co-registration operation between the substantially co-located optics subsystem and radar subsystem, the co-registration operation comprising: obtaining, from the radar subsystem, radar measurements of radar calibration objection object positioned at a far-field range; obtaining, from the optics subsystem, optical measurements of an optical calibration object configured to provide an optical signal at spectral band(s) detectable by the optics subsystem; utilizing said radar measurements and said optical measurements to determine co-registration between a direction of the radar subsystem and a direction of the optics subsystem; and wherein said optical calibration object is light emitter providing modulated light; and wherein said co-registration operation comprises image processing utilizing said modulation to determine position of the optical calibration object, said image processing comprising performing a difference between at least two different images of the optical calibration object acquired by the optics subsystem located at the first position, to reduce errors induced by atmospheric path turbulence and/or for optical aberrations of the optics subsystem. 